Hi Kirt,

i already tried adding Sb2O3 as surfactant, surfaces were mirror like, so
surfactant was working well.

Agitation was realized with a magnetic stirrer, but was not so strong. I'm
afraid that strong agitation may destroy membranes.
Ok, if etching at room temperature will not work i will try with ultrasound.

In any case i need to realize just 4-5 membranes, and i have a lot of time
to realize them, so i can accept to realize etching at room temperature.

Best regards,
Andrea


> Andrea--
>
> Your etch-rate variation across the membrane sounds like a typical case of
> loading. The KOH/H2O is probably being depleted from the region in the
> center faster than the region at the edges, where more KOH/H2O can flow in
> from the side. This is common in both wet and dry etching that is
> transport-limited, and is more profound in larger etch holes--5x5 mm is
> indeed large. In addition, it is possible that bubbles at the center are
> blocking the flow of etchant in and etch product out. Things that can help
> uniformity are agitation of the wafer, circulation of the liquid, addition
> of surfactant, and possibly ultrasound.
>
>    --Kirt Williams